1. Field of the Invention
This invention relates to electrically controlled panes, the coloration and/or transmission state of which in certain wavelengths of electromagnetic radiation, notably in the visible range, varies under the effect of an electrical current. More specifically, the invention concerns electrochromic panes based upon a film of a transition metal oxide capable of reversibly inserting cations, the oxidation states corresponding to the inserted and deinserted states having different properties of coloration and/or light transmission.
2. Discussion of the Background
Most commonly, electrochromic panes comprise, as principal functional film, a film of tungsten oxide WO.sub.3, a cathodic electrochromic material, which is colorless when the tungsten is in its maximum oxidation state (+6) and dark blue for an oxidation state less than 5, for which the cation insertion reaction can be written: EQU WO.sub.3 (a)+xM.sup.+ +xe.sup.- .revreaction.M.sub.x WO.sub.3 (b)
where M.sup.+ =Li.sup.+, H.sup.+ etc . . .
For good reversibility of coloration, a cation source, itself preferably constituted of a film of electrochromic material, should be associated with the tungsten oxide film. The contrast is certainly reinforced if a coloration material known as anodic is used. Contrary to tungsten oxide, an anodic coloration material is colored in the deinserted state. Between the two films of electrochromic material there is interposed an electrolyte as a cation transfer means. Finally, the system should be completed by electron conducting films for the supply of electric current.
Electrochromic panes, sometimes termed intelligent panes, are particularly interesting for controlling the input of solar radiation in regions where the sunshine varies widely throughout the year. It is desirable to have available, at certain times, a very effective antisolar pane, which is accompanied by a very pronounced dark coloration and, at other times, a pane which in contrast is very clear, to allow good illumination by natural light.
However, electrochromic panes have isotropic optical properties for all directions of incidence of the radiation. Now in practice, all these directions are not equivalent: it is self-evident that the principal source of the energy radiation reaches the pane most often at a large angle of incidence, above the horizontal. In contrast, the view of the occupant of the building will most commonly be directed at an angle along the plane perpendicular to the pane or downwards. On the other hand, the reduction in the light transmission that accompanies any reduction in the energy transmission is usually considered as an unavoidable, but nevertheless unpleasant, defect of antisolar panes. From these aspects, it would be desirable for the pane to have a certain angular selectivity, that is to say for its optical performances to be strengthened according to the direction of incidence of the electromagnetic radiation.
French Patent Application FR-2 698 093, corresponding to EP-A-0 598 660 and U.S. Ser. No. 08/153,909, instructs about a pane, the transmission properties of which vary as a function of the incident light, produced by cathodic sputtering of a target of metal alloy--notably of the nickel-chromium or tantalum type, a guide channelling the particles emitted by the target to direct them obliquely onto the plane of the substrate. This method makes it possible to obtain, on an industrial scale, thin films having a structure which may be qualified as pseudo-columnar, the axes of growth of the crystals being parallel to straight lines contained within a dihedron of narrow opening (of small dihedral angle), the bisector plane of which makes an acute angle with the substrate.
This process makes possible the obtaining of panes having good optical selectivity as a function of the direction of observation. For all that, these panes still remain passive panes with fixed optical properties: the optical performances of these panes are optimized for quite precise sunshine conditions, which is far from being perfect for regions in which solar conditions continually vary.
The invention has as its objective an electrochromic pane which, in one of its coloration states, has a strong anisotropy of its transmission characteristics for electromagnetic radiation.